It is known in the art to chance the economy of transport facilities by full loading the engine under all operating conditions. This is done, in particular, by developing more flexible transmission systems, by designing gear-boxes varying in the structural schemes and operating principles that permit controlling the loading of the engine depending on constantly varying external loads.
Mechanical fixed-ratio gear-boxes, most widely spread at present, mainly comprise a drive shaft, a driven shaft and an intermediate shaft, a set of gear-wheels, synchronizers and a gear-shifting mechanisms (V. I. Platonov "All-wheel-drive automobiles", 1969, Mashinostroenie Publishers, Moscow, p. 92, FIG. 26).
This type of transmission features a high efficiency and, to enhance the performance characteristics of automobiles, there is a tendency to improve the fixed-ratio gear-boxes by increasing the number of gears and removing discontinuity in the engine power stream in gear changing.
The solutions directed at increasing the number of gears in mechanical gear-boxes are, for example, SU Patent No. 1362882, 1986, and SU Patent No. 1131685, 1983. The gear-box of SU Patent No. 1362882 comprises a drive shaft and a driven shaft that carry gear wheels freely rotatable thereabout and engagable in pairs. Disposed between the gear wheels are five-position clutches that connect the gear wheels to each other and to the shaft. By varying the setting of the clutches and choosing the combination of their positions, it is possible to obtain a greater number of transmissions as against a conventional design with the same number of gear wheels.
Also known is a gear-box with an increased number of gears and a higher efficiency wherein gear-changing is ensured without discontinuing the power stream (SU Patent No. 1131685). Such a gearbox comprises two concentric primary shafts driven from two clutches, an intermediate shaft and a secondary shaft, gear wheels and couplings mounted on said shafts, said couplings connecting the gear wheels with the shafts. In order to transmit the power stream from the engine to the secondary shaft, two kinematic chains can be formed in such a design, and in order to shift gears without breaking the power stream, it is required, during operation of one kinematic chain from one of the clutches and from one of the primary shafts, to connect the second kinematic chain to the secondary shaft from the other clutch and the other primary shaft, and then to effect gear shifting by a smooth change of the clutches with overlap.
Increasing the number of gear wheels and introducing multiposition couplings, and thus making it possible to vary the pattern of connection of these gear wheels, are to some extent conducive to increasing the number of gears and excluding discontinuities in the power stream. This way, however, does not allow designing a conventional mechanical gear-box capable of readily responding to variations of an external load by instantaneously selecting the most favourable gear ratio for the most stable loading of the engine.
A gear-box is also known (SU Patent No. 444025, 1975), which comprises a drive shaft which carries concentrically mounted gear wheels, one on the cylindrical surface of the other, connected with each other through controlled clutches and having inner and outer ring gears, a casing accommodating concentric gear wheels freely rotatably and axially movably therein. It also has inner and outer ring gears arranged eccentrically with respect to said gear wheels and concentrically fitted on the drive shaft. In order to effect engagement of the outer and inner ring gears of some gear wheels respectively with the inner and outer ring gears of the other gear wheels, the gear-box is provided with control sliders, mounted in the casing, that shift that part of the gear wheels mounted on the casing which corresponds to the required gear, into a position of engagement with the ring gears. Placed between the ring gears of the wheels fitted on the drive shaft, of which the central wheel is connected with this shaft and the outer wheel is connected with a driven shaft, are control rods that are acted upon when the wheels mounted on the casing move axially so that the clutches are unlocked and, correspondingly, the required transmission is put in gear.